1. Field of the Invention
The present invention relates to a process for producing substituted benzoic acids useful as intermediates for medicaments or agricultural chemicals, e.g., herbicides.
2. Description of the Prior Art
lt has been known that substituted benzoic acids can be produced by a process in which a substituted toluene is subjected to oxidation with an oxidizing agent, e.g., permanganates.
In the known process, however, oxidizing agents must be used in large excess, and the desired substituted benzoic acids can be produced at only a poor yield, e.g., as low as 40% or less. In addition, it is required to treat large quantities of waste water and manganese-containing wastes. Accordingly, the process is by no means suited for commercialscale production of substituted benzoic acids.
It has also been known that aromatic carboxylic acids can be produced from alkylbenzenes, such as toluene and xylene, by subjecting the latter to autoxidation with an oxygen-containing gas in the presence of a catalyst, such as cobalt acetate (see J. Am. Chem. Soc., 91, p. 6380 (1969).
However, it has not been known that toluenes having substituents at 2- and 6-positions thereof undergo autoxidation with an oxygen-containing gas. This may be attributable to the fact that it was generally presumed that autoxidation of 2,6-disubstituted toluene with an oxygen-containing gas would hardly proceed because of steric hindrance and electronic effects caused by the substitutional groups at the 2- and 6-positions thereof.
The present inventors have conducted intensive investigations on the autoxidation of substituted toluenes with an oxygen-containing gas and, as a result, have completed the present invention.